Use pythonpath from autoconf in python utils
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This merge request is automatically copied from !313 (merged) orginally made by @andrii
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Python3-compatibility rewrite made both arcctl
and arcconfig-parser
autoconf-substituted. They cannot be used as-is directly from the source tree without configure
anyway, so we can substitute more things painlessly.
As of now, pythonpath will be substituted in python code as well.